This invention relates to a support apparatus for external mounting on a well casing or other cylindrical member of circular cross-section and, more particularly, to a packing support for mounting on a well casing to support a packing which seals the annulus between the casing and the wellhead or the bore wall of an outer casing.
To secure structures such as packing assemblies to the exterior of a casing or tubing, it is sometimes desirable or necessary to provide a support therefor which can be secured to the casing without piercing the casing wall or welding thereto and without attachment to an external support such as, for example, a wellhead or an outer casing. This latter feature is particularly important with packing assemblies which are used for sealing between a casing and a wellhead such as a geothermal wellhead wherein the casing will characteristically move longitudinally within the wellhead in response to thermal conditions and temperature changes associated therewith. It is also essential when used as a packing support that the packing support assembly grip the casing very securely and be immovable thereon since such packing are usually subjected to very great compressive forces.
Heretofore, packing supports have been utilized that encompass a single annular ring sleeved about a well casing and secured in place by a plurality of set screws directed radially inwards towards the casing. However, these supports have frequently been unable to sustain an adequate grip on the casing due to the extreme pressures and forces present in a geothermal well. Packing supports which are capable of withstanding these high forces have been designed and an example of such a packing support is shown in U.S. patent application Ser. No. 315,275 filed Oct. 26, 1981, U.S. Pat. No. 4,372,563, by Robert J. Diehl et al. The packing support shown therein utilizes two annular rings adapted to be sleeved about a casing for supporting a plurality of packing elements thereon. A first ring is initially secured to the casing with set screws and has deformable gripping fingers. The fingers are wedged radially inward to further secure the packing support to the casing by means of a second ring which is threaded onto the exterior of the first ring. The gripping force is determined by the amount of rotation of the second ring relative to the first ring. However, under certain service conditions it is difficult to obtain a secure attachment of the packing support to the casing due to the extremely high rotational forces required to wedge the fingers to a secure engaging relationship with the casing. Also, on occasion, the set screws initially holding the first ring to the casing break loose because of the high rotational forces required to seat the second ring onto the gripping fingers of the first ring thereby allowing both rings to rotate about the casing and creating an unsecure packing support apparatus.